The Hollerith Card

1890 · Round-Hole Card · Work 574 of 1,871

The Hollerith Card, 1890, Round-Hole Card

A single buff card the size of a dollar bill, printed with a grid of coded fields and pierced with round holes, the printed headings reading as abbreviations rather than words.

What it was used for
The Hollerith card was the data carrier of the 1890 United States census: a piece of thin manila pasteboard, according to the eyewitness T. C. Martin 6⅝ inches long and 3¼ inches high, with the lower corner clipped so that it could not lie the wrong way round in the machines. Its whole face was divided into 24 columns of quarter-inch squares, 288 positions in all. The four columns at the left were reserved for the geographic identification and were punched by a machine of their own, the gang punch, several cards at a time for each district; the remaining 240 positions carried the particulars of the person. The holes were round. One card stood for one human being.
What was new
What was new was that the card itself became the method of calculation: position on the sheet was meaning, and writing was no longer needed. That is exactly where the catch lies. The 1890 cards were unprinted - what a position meant stood on the punch's face plate and on a reading board. Truesdell records the result: the difficulty of reading the blank cards seemed to prove "a serious disadvantage", and all later census cards were printed. The card was thus machine-readable before it was human-readable. Its format did not last: from 1907 the 45-column card became the industry standard, in 1928 the 80-column card. The Census Bureau itself only moved to the 45-column card in 1940, chiefly because it provided space for additional fields.

What the sources leave open: The legend that the card's size was that of the US banknote is asserted without qualification by Columbia University, by the Computer History Museum with "roughly", and by Douglas W. Jones with "apparently" and expressly for the later 7⅜-inch card. For 1890 the arithmetic fails: the large-size notes measured 7.50 by 3.125 inches, the card 6.625 by 3.25. No source contradicting the legend was found. The hole diameter is not documented.

Further reading